The invention relates to a system including a tactile pressure sensor with an opaque cylindrical body which consists of an elastomer and has several axially extending bores, and an image receiving apparatus with a data processor. The pressure sensor responds to a pressure applied to its tactile part with a light intensity change. This light intensity change is transmitted, by way of a light transmission structure, to an image receiver and is recorded. A data processor connected to the image receiver controls the image receiver and reads the intensity-relevant data. The pressure effective on the pressure sensitive surface can then be displayed or control signals can be transmitted to associated operating equipment or sensing devices.
Such pressure sensors have various applications. They may be used for example as touch-sensitive devices in the robot technology. They can be used for sensing surface conditions. In the medical field, tissue areas or organs can be probed.
A company "Interlink" utilizes a pressure array in a laparoscopic grasping clamp in order to obtain pressure data. The sensor comprises a semi-conductive polymer, which changes its resistance when subjected to external pressure. These pressure data which are suitable only for a dynamic pressure determination are, after a graphic display on a PC monitor, returned to a tactile system (see Fischer, H. et al, "Messungen der Greifkrafte chirurgischer Zangen mit FSRTM-sensors" internal report, Forschungszentrum Karlsruhe, HIT, 1994). The semi-conductive polymer has the disadvantageous property that it ages very rapidly if used frequently, exhibits a very high creep behavior and is therefore not suitable for static pressure measurements since the inference regarding the pressure generated becomes incorrect.
Very common are tactile capacitive foil sensors. They generally consist of two copperstrips which are disposed crosswise on top of each other and are separated by a dielectric elastomer such that they form a condenser matrix (see J. Seekircher et al. "Improved Tactile Sensors", selected papers from the 2.sup.nd IFAC symposium, Pergamon 1989, p. 317-322). The pressure on the sensor is transformed to a capacity change. However, such an arrangement is very susceptible to electric fields since the signal value is very small because, with a layer thickness of 30 .mu.m, the capacity changes of 0.6 pF at d/d=10% are very small.
DE 32 36 435 C2 discloses a fiber optic sensor, wherein light is conducted through a tube whose open width is pressure dependent and determines the intensity of light conducted through the tube to a receiver. With such a sensor, however, no layer arrangement can be provided since it is different in principle.
A pressure intensity transmission arrangement, which permits the construction of tactile sensors of small dimensions and with high resolution for the installation into a finger of a robot clamp is described by D. H. Mott et al. FIG. 1 on page 181 shows the principle of the conversion of the pressure intensity into light intensity in ROBOT SENSORS, Volume 2, Tactile and Non-Vision, edited by Prof. A. Pugh, Springer Volag Berlin, Heidelberg, New York, Tokyo, 1986 in the contribution "An Experimental Very High Resolution Tactile Sensor Array", on pages 179 to 188.
The tactile part includes a transparent acrylic plate on which, separated by an air space, a foil in the form of a resilient membrane is disposed. From the side, light is radiated into the acrylic plate, which passes through the plate when there is no load on the plate. The light is reflected on the side walls and exits at the opposite front wall. If the membrane is pressed by outer pressure inputs at any place into contact with the acrylic plate the light reflection in the contact area becomes diffuse because the fraction index changes and light radiates out through the side wall.
The image of the light which is reflected from the tactile sensor in a diffuse manner is directed, by means of optical equipment onto the entrance surface of a CCD chip with a lens disposed in front thereof and is then further processed in a data processor connected to the chip for the display of the video signals or for the generation of control signals for the robot clamp. Also, the CCD camera is controlled and operated by the data processor. Only video images are produced which are generated by a lens system disposed in front. The force applied cannot be determined with this system.
The video images normally produced with CCD chips generally need to be subsequently analyzed by expensive image recognition methods since very large amounts of data are available with for example 486 923 pixels. If PC analyzing units are utilized, the large amount of data which are generated during translation movement in serial cut sections can be used. However, with the hardware utilized in the CCIR standard (international TV standard), there is no data reduction. Such reduction has to be implemented during later processing by expensive software programs. As a video unit the total system is fast but the data processing between the intensity measurement of the light distribution on the CCD chip requires a lot of time. Standard CCD processing provides only visual images without coordination in the form of a voltage signal of the pressure, or respectively, the light intensity effective on the sensor. They serve generally for the visual recognition of objects (textures, outlines).
U.S. Pat. No. 4,599,908 discloses a pressure sensor with a cylindrical body of an elastomer, which includes several axially extending bores. In this sensor, the light is coupled by way of wave guides into the sensor and is reflected at the pressure sensitive end of the sensor in a pressure dependent manner.
It is the object of the present invention to provide a sensor with which static and dynamic pressure distributions on bodies or other objects can be measured in a small surface area in an absolute and dynamic way. A system should be utilized for this purpose comprising a pressure sensor and an imaging device with a data processor. With this system, it should be possible to represent the "finger tip feel" graphically on a monitor. Furthermore, such a system should be suitable for controlling actuators.